1. Field of the Invention
The present invention relates to a lens driving device of a small camera mounted on a mobile phone or the like.
2. Description of the Related Art
Recently, mobile phones have become widely used, and their functions are improved, and the one provided with a small camera enters the mainstream. Hereinafter, a lens driving device of the small camera will be described with reference to the drawings (e.g., refer to, Unexamined Japanese Patent Publication No. 2008-33252).
FIG. 9 is an exploded perspective view of a conventional lens driving device. FIG. 10 is an external perspective view of the conventional lens driving device. FIG. 11 is a cross-sectional view of the conventional lens driving device. In addition, FIG. 11 is a simplified cross-sectional view taken along line 11-11 in FIG. 10. This lens driving device has base 201, lower spring 205, carrier 210, coil 12, yoke 15, insulation spacer 14, magnet 20, upper spring 22, and cover member 25.
Base 201 is formed into a rectangular shape in a top view, and has a hole in its center. First projection 2 is formed to be integral with base 201 and extends upward from an upper surface of each one of four corners of base 201. Base 201 is made of an insulating resin.
Two lower springs 205 are arranged on the upper surface of base 201 so as not to be overlapped with each other, and electrically independent to each other. A surrounding part of lower spring 205 is fixed to base 201. A part of the surrounding part is bent downward to provide terminal 206. In addition, two elastic arms are formed so as to extend between the surrounding part and lower holding part 7. Lower holding part 7 of lower spring 205 is fixed to a lower part of carrier 210.
Carrier 210 is roughly cylindrical. Annular coil 12 is fixed to an outer periphery of carrier 210. Respective end parts of a wire of coil 12 are connected to respective lower springs 5. Insulation spacer 14 is put on lower spring 205. Yoke 15 is formed into a roughly octagonal shape, in a top view, which is provided by chamfering corner parts of a rectangle. Yoke 15 is formed into a box shape having an opening on the lower side. Yoke 15 is put on insulation spacer 14. Yoke 15 houses carrier 210 to which coil 12 is fixed, on the inside of its outer walls. Four magnets 20 are fixed on the inside of the four chamfered corner parts of yoke 15, respectively.
Magnet 20 has, in a top view, first outer surface 20A, second outer surface 20B, and third outer surface 20C which are opposed to three inner surfaces of the adjacent outer walls at each one of the four corners of yoke 15. In addition, arc-shaped surface 20D is provided on the inner side so as to connect first outer surface 20A to second outer surface 20B provided on both ends of third outer surface 20C. Thus, each magnet 20 is bonded and fixed to yoke 15 in such a manner that first to third outer surfaces 20A to 20C abut on the three inner surfaces of the adjacent outer walls of yoke 15, respectively. In the fixed state, each magnet 20 is configured such that the north pole (or south pole) is provided on the side of arc-shaped surface 20D in an entire height direction, and the south pole (or north pole) is provided on the sides of first to third outer surfaces 20A to 20C in an entire height direction. That is, it is configured such that the different poles are provided between the side of arc-shaped surface 20D and the sides of first to third outer surfaces 20A to 20C. Arc-shaped surface 20D of magnet 20 is opposed to the outer periphery surface of coil 12 with some space therebetween.
Upper spring 22 is arranged on an upper surface of yoke 15. Upper spring 22 is provided with four elastic arms extending from its outer frame part toward its inner periphery side and having the same shape. One end of the elastic arm is connected to upper holding part 23 formed into a circular ring. Upper holding part 23 is fixed to an upper part of carrier 210.
Cover member 25 is arranged on upper spring 22. Cover member 25 is formed into a rectangular shape in a top view, and has a hole in the center. Second projection 26 is formed to be integral with cover member 25 and extends downward from each one of four corners thereof. Cover member 25 is made of an insulating resin. An outer frame part of upper spring 22 is fixed between cover member 25 and yoke 15.
Second projection 26 of cover member 25 and first projection 2 of base 201 are positioned outside the chamfered corner position of yoke 15. Upper second projection 26 and lower first projection 2 vertically abut on each other, and their abutment parts are bonded and fixed to each other. Similarly, four second projections 26 and four first projections 2 are all bonded and fixed, respectively.
The conventional lens driving device configured as described above is mounted on equipment after a lens barrel having a lens is mounted on carrier 210.
When a voltage is applied between terminals 206 of two lower springs 205, a current flows in coil 12. Thus, a current flows in coil 12 in a direction perpendicular to magnetic flux from magnet 20. As a result, force acts on coil 12 in the vertical direction as the current flows. Thus, carrier 210 fixed to coil 12 is moved in an upper direction or a lower direction (optical axis direction). Carrier 210 is moved and stopped in an upper position or a lower position in which spring force of the elastic arm of lower spring 205 is proportional to that of upper spring 22. By controlling the voltage applied between terminals 206, that is, the current flowing in coil 12, the vertical movement of carrier 210 can be controlled. As a result, a position of the lens barrel integral with carrier 210 can be adjusted.
Yoke 15 has the roughly octagon shape provided by chamfering its rectangle corner parts, in the top view. Second projection 26 of cover member 25 abuts on and bonded to first projection 2 of base 201 on the outside of the chamfered corner part. However, in this configuration, first projection 2 and second projection 26 are bonded to each other only at their end faces in the vertical direction. In order to obtain predetermined bonding strength, an area of the bonded part has to be surely ensured, so that it is necessary to thicken first projection 2 and second projection 26. However, to thicken second projection 26 and first projection 2, the chamfered part of yoke 15 needs to be large, so that space in yoke 15 is reduced due to the chamfered part. Thus, it is difficult to ensure the space for magnet 20 to be arranged in yoke 15.